Let,
the number of guppies be x
the number of goldfish be y
Since, Ben has 3 times as many guppies as goldfish, we can write,
x = 3y.............................equation (1)
Also,
It is given that he as total of 20 fish. So, we can say that,
x + y = 20
3y + y= 20..........substituting value of x from equation (1)
4y = 20
Divide both sides by 4 to get y by itself,
y = 20 / 4
y = 5
Now,
x = 3y
x = 3 * 5
x = 15
Since, number of guppies is x, we can say that he has 15 guppies
